Where does the Spinalis muscle originate?

The Spinalis muscle is part of the erector spinae group, which works primarily to extend and laterally flex the spine. Its origin is specifically from the posterior iliac crest, sacrum, and the spinous processes of the lumbar vertebrae, distinguishing it from other muscles related to the spine. The correct choice emphasizes the broad tendon's origin from the posterior iliac crest, indicating that it starts in the lower back area and contributes to the overall functioning and stability of the spine.

The origin from the posterior iliac crest is significant as it helps in maintaining upright posture and supporting the trunk during various movements. Understanding this origin can help clarify the muscle's role in spinal extension and lateral movement. The other options suggest origins that do not align with the Spinalis muscle's anatomical and functional characteristics, reinforcing why the selected choice is accurate.